硅基GaN垂直结构功率二极管外延材料的缺陷抑制与可控掺杂研究

GaN power diodes will have significant applications in high temperature, high pressure and high frequency power electronics. Current GaN free-standing substrates are quite expensive and limited in wafer size, which results in high cost of homo-epitaxial GaN power diodes. Using large-size Si substrate to grow GaN vertical power diodes is expected to substantially reduce costs. Now the epitaxial growth of GaN vertical power diodes on Si substrates has the following key challenging issues. (1) It is quite difficult to grow high quality and thick GaN films on Si substrates due to the large mismatch stress and the high defect density, which adversely affects the device breakdown voltage (BV). (2) Reproducible growth of high quality GaN drift region with a low and controllable carrier concentration is not readily available due to the high concentration of point defects, such as Si, C, and O impurities and vacancy defects, which has a negative effect on the device performance such as the BV and the conduction loss. Given our present work in this field, this project will aim for the defect reduction and doping control for GaN vertical power diode grown on Si substrates. Mask-free GaN epitaxial lateral overgrowth technique will be used to remarkably improve the crystal quality, the thickness and the BV of GaN epilayer on Si substrate. A combination of electrical, optoelectronic, and microstructural characterization techniques will be used to study the electrical properties of various defects, as well as their influence on device performance, and thereby to further reduce the density of critical defects in GaN epilayer and enable repeatable and controllable doping. This work will lay the core material foundation for high performance, low-cost GaN vertical power diodes.

GaN功率二极管在高温、高压、高频功率转换领域具有重要应用价值。目前GaN自支撑衬底尺寸小、价格昂贵，同质外延的器件成本居高不下；采用大尺寸Si衬底异质外延有望大幅降低成本。目前Si基GaN垂直结构功率二极管的外延生长存在以下关键问题：1）应力大、缺陷密度高，难以获得高质量GaN厚层，影响器件耐压特性；2）漂移区的载流子浓度受Si、O、C等杂质和空位等缺陷密度影响，难以实现重复可控，影响器件耐压与导通损耗等性能。在已有的工作基础上，本项目拟深入研究Si基GaN功率二极管外延材料中的缺陷抑制与可控掺杂，通过无掩模的GaN侧向外延技术来显著提升Si基GaN外延材料的晶体质量与厚度以及器件耐压，采用多种电学、光电、及微结构表征来研究缺陷的电学性质及其对器件性能的影响，从而进一步降低材料的关键缺陷密度并实现掺杂的重复可控，为实现高性能、低成本GaN垂直结构功率二极管奠定核心材料基础。

氮化镓（GaN）垂直结构功率二极管具有体积小、击穿电压高、导通损耗小、功耗低等显著优势，在高温、高压、高频开关器件应用领域具有重要价值。本项目以低成本、高性能的硅衬底GaN垂直功率二极管需求为牵引，从材料层面深入挖掘限制器件性能的关键科学问题，通过研究硅基GaN功率二极管外延材料中的缺陷抑制与可控掺杂，来显著提升硅基GaN垂直功率二极管的材料质量与器件耐压等。主要成果包括：.(1) 阐明了硅基GaN异质外延生长中应力与位错缺陷的相互作用机制，国际首次实现无裂纹10 μm厚的硅基GaN薄膜，位错密度降低至5.8×10^(7)cm(-2)，低于国际同行1~2个数量级。.(2) 成功研制出高性能的硅基GaN垂直SBD功率器件，器件Baliga优值BFOM高达0.26GW/cm2，为硅衬底GaN垂直SBD器件公开报道的最新记录，并揭示了有/无离子注入保护终端的垂直SBD中点缺陷相关的漏电和击穿机制。.(3) 拓展研究了硅基GaN高质量激光器材料的外延生长。通过杂质和空位点缺陷抑制，成功将硅基GaN激光器的阈值电流密度由4.7降低至2.25kA/cm2，阈值电压由8.2V降低至4.7V，并实现了国际首支室温电注入工作的硅基GaN超辐射发光二极管。.(4) 拓展研究了硅基AlGaN紫外光电子材料生长中的应力调控与缺陷抑制。成功实现了无裂纹2 μm厚的硅基Al0.5Ga0.5N深紫外材料，为低成本的硅基AlGaN深紫外LED和探测器等的研究奠定了坚实的材料基础。. 综上，本项目突破和掌握了硅基GaN高质量材料的缺陷抑制及轻掺杂载流子浓度重复可控等核心外延技术，积极拓展研究并实现了高性能的硅基GaN垂直SBD器件，对进一步研究硅基GaN结势垒肖特基二极管等纵向功率器件具有重要指导意义，为推动我国自主可控的高性能硅基GaN纵向功率器件的研发奠定了坚实材料基础。上述相关成果被Semiconductor Today等国际半导体专业媒体多次跟踪报道。在本项目资助下，共发表学术论文15篇，其中第一/通讯作者7篇；共申请发明专利9项，其中1项已授权。培养博士后1名，研究生3名，其中毕业博士2名，毕业硕士1名。圆满完成了预期的研究目标。